In Microsoft Exchange Server 2007, there are five server roles that you can install and then configure on a computer that is running Microsoft Windows Server 2003. This topic provides an overview of the Client Access server role. The Client Access server role supports the Microsoft Outlook Web Access and Microsoft Exchange ActiveSync client applications and the Post Office Protocol version 3 (POP3) and Internet Message Access Protocol version 4rev1 (IMAP4) protocols. The Client Access server role also supports services, such as the Autodiscover service and Web services.

The Client Access server role accepts connections to your Exchange 2007 server from a variety of different clients. Software clients such as Microsoft Outlook Express and Eudora use POP3 or IMAP4 connections to communicate with the Exchange server. Hardware clients, such as mobile devices, use ActiveSync, POP3, or IMAP4 to communicate with the Exchange server. The Client Access server role is required in every Exchange Server 2007 organization.

Outlook Web Access in Exchange Server 2007 lets you access your e-mail from any Web browser. Outlook Web Access has been redesigned in Exchange Server 2007 to enhance the user experience and productivity in many ways. New features, such as smart meeting booking, Microsoft Windows SharePoint Services and Universal Naming Convention (UNC) file share integration, and improvements in reminders and the address book, give you a rich user experience from any computer that has a Web browser. There are two versions of Outlook Web Access included in Exchange Server 2007: the full-featured Premium Outlook Web Access client and the new Outlook Web Access Light client. Outlook Web Access Light is designed to optimize your Outlook Web Access experience for mobile devices and slower connections.

For more information about Outlook Web Access, see the following topics:

If you use a device that has Windows Mobile 5.0 and the Messaging Security and Feature Pack (MSFP) installed, your mobile device will support Direct Push. Direct Push is a technology that is built into Exchange ActiveSync that keeps a mobile device continuously synchronized with an Exchange mailbox.

For more information about Exchange ActiveSync, see the following topics:

Besides supporting MAPI and HTTP clients, Exchange Server 2007 supports POP3 and IMAP4 clients. By default, POP3 and IMAP4 are installed when you install the Client Access server role. However, the services that are needed to support POP3 and IMAP4 are disabled. To use POP3 and IMAP4, you must start the POP3 and IMAP4 services.